Download Genetics Practice III

Genetics Practice III
1. In tomatoes the texture of the skin may be smooth or peach (hairy). The
Ponderosa variety has fruits with smooth texture. The red peach variety has fruits
with peach texture. Crosses between the two varieties produce all smooth fruits.
Crosses between these smooth fruited F1 plants produced 174 peach textured
fruits and 520 smooth textured fruits. What is the mode of inheritance for this skin
texture? Draw the Punnett squares that illustrate these crosses.
2. In cattle, reddish coat color is not completely dominant to white coat color.
Heterozygous individuals have coats that are roan colored (ie. reddish, but with
spots of white hairs). Outline a breeding procedure whereby a true breeding
strain of red cattle could be established from a roan bull and a white cow.
3. The X-linked barred locus in chickens controls the pattern of the feathers, with
the alleles B for barred pattern and b for no bars. If a barred male (XB Y) is mated
to a nonbarred female (Xb Xb), what will be the appearance of the male and
female progeny?
4. Suppose a father and mother claim they have been given the wrong baby at
the hospital. Both parents are blood type A. The baby they have been given is
blood type O. What evidence bearing on this case does this fact have?
5. Shaggy hair in dogs is dominant to its recessive allele, short hair, and black
coat color is dominant to its recessive allele, tan. What are the genotypes of the
parents if their phenotypes are one black, shaggy-hair and short-haired tan, and
the progeny exhibit following phenotypes: 46% shaggy and black, 44% short and
tan, 5% shaggy and tan and 5% are short and black. Show the Punnett Square
that illustrates this.
6. Use the Punnett square to determine all of the offspring genotypes from the
following crosses (Just set up and solve. Don’t do genotypic ratios):
a. RrYy x RrYy
b. RrYy x rryy
c. RrYy x Rryy
7. In the problem above, the "R" allele is a dominant allele specifying for round
seeds (in peas), while the "r" allele is the recessive allele specifying for wrinkled
seeds; in addition, the "Y" allele specifies for the dominant yellow seed color trait,
while "y" specifies for green seeds (recessive). Give the expected frequencies
(as percentages or ratios) for the phenotypes of the offspring resulting from each
of the crosses above.
8. In turkeys a dominant gene R produces the familiar bronze color; its recessive
allele r results in red. Another dominant gene H results in normal feathers; its
recessive allele h produces feathers without webbing, so that they resemble tufts
of hair. Two bronze turkeys with normal feathers were mated, and their offspring
consisted of 8 bronze with normal feathers, three bronze with hairy feathers, two
red with normal feathers, and one red with hairy feathers. What were the
genotypes of the parents?
9. The Agouti Gene is the principal coat color gene in the Shetland Sheepdogs
(Sheltie), producing sable or black coats. There are at least two other genes that
influence shading and patterns in the coat. The three alleles of this gene are:
ay - sable coat color
at - tricolor - black coat with tan points
ab - bicolor - black coat
Each individual has two copies of each gene, thus: a y-ay pure for sable
shelties usually have golden sable coats (Brown heads). ay-at and ay-ab Shelties
usually have sable coats with some extent of black and are referred to as shaded
sables (Brown heads with black shading) (and also, confusingly, as trifactored
sables). at-at and at-ab shelties are Tricolored (Black, Brown and white heads).
ab-ab Shelties are Bicolored (Black and white head).
Show the genotypes and phenotypes that would result from a cross between
the following parents:
ay at X at ab
References:
http://www.athro.com/evo/gen/sheltie.html
http://www.zerobio.com/drag_gr11/sexlink.htm
http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html